1. Field of the Invention
The present invention relates to a vacuum film-forming apparatus or device, in particular, to a vacuum film-forming apparatus (an atomic layer deposition apparatus), which forms a thin film according to the ALD technique (Atomic Layer Deposition Technique).
2. Description of the Prior Art
Recently, the patterns of semiconductor integrated circuits have increasingly been finer and it has correspondingly been devised that fine contact holes, trenches and other similar structures having high aspect ratios have been filled up with a distributing wire material such as Cu and/or Al. If the aspect ratio increases in this manner, it would be difficult to fill up such holes and/or trenches with a conductive film in a good or high coverage.
When using, for instance, Cu as a principal distributing wire material in the case of the foregoing embedded distributing wire structure, deposited Cu may easily diffuse into the neighboring insulating film and this becomes a cause of various defects and troubles. For this reason, a conductive barrier film is formed between an insulating film and such a conductive film to thus inhibit or control any possible diffusion of Cu. There have been proposed various methods for forming such a barrier film and there has been known, for instance, a method which comprises the step of forming a barrier film by depositing a layer of a material such as Ta, TiN, and/or TaN while using, for instance, the ALD technique (see, for instance, Japanese Un-Examined Patent Publication 2004-6856 (see, for instance, claims)).
The ALD technique is similar to the CVD technique in that it makes use of a chemical reaction between precursors. However, they differ from one another in that the usual CVD technique makes use of such a phenomenon that two kinds of gaseous precursors are brought into contact with one another to thus cause the reaction between them, while the ALD technique makes use of a surface reaction between two precursors. More specifically, the ALD technique comprises the steps of forming a desired metal film by supplying one of two precursors (for instance, a reactant gas) onto the surface of a substrate on which the other precursor (for instance, a raw gas) has been adsorbed to bring these precursors into contact with one another on the substrate surface and to thus cause a film-forming reaction between them. In this case, the precursor preliminarily adsorbed on the substrate surface undergoes the reaction with the precursor subsequently supplied to the surface at a quite high reaction rate on the substrate surface. In this respect, such precursors may be in the form of, for instance, solids, liquids or gases and the raw gas is supplied together with a carrier gas such as N2 or Ar. As has been described above, the ALD technique is a film-forming method which comprises alternatively repeating a step of adsorbing a raw gas on a substrate surface and a step of allowing the adsorbed raw gas to react with a reactant gas to thus form a film in an atomic level. More specifically, these precursors always undergo such adsorption and reaction within a superficial moving region and accordingly, this technique would ensure the considerably high step-coverage characteristics. In addition, the raw gas is allowed to react with the reactant gas while separately supplying these gases and therefore, it can improve the film density. For this reason, this technique has attracted special interest recently.
A conventional atomic layer-depositing apparatus (ALD apparatus) in which a thin film is formed according to the foregoing ALD technique comprises a film-forming unit or chamber provided with an evacuation means and it further comprises a stage for supporting a substrate (hereunder referred to as “substrate stage”), which is equipped with a heating means and disposed within the film-forming chamber, and a gas-introduction means disposed on the side opposite to the substrate stage and arranged on the ceiling of the film-forming chamber. As such an ALD apparatus, there has been known, for instance, one which is so designed that a thin film having a desired thickness can be prepared by separately and periodically supplying a desired raw gas and a desired reactant gas into the apparatus through a gas-introduction means to thus repeat a raw gas-adsorption step and a plasma-assisted reaction step for allowing the raw gas to react with the reactant gas by the aid of the plasma (see, for instance, Japanese Un-Examined Patent Publication 2003-318174 (see, for instance, claims)).
More specifically, it has been known that when forming a ZrB2 film as a barrier layer using Zr(BH4)4 as such a raw material, such a barrier film can be formed according to the following reaction equations (1) and (2):Zr(BH4)4→ZrB2+B2H6+5H2  (1)Zr(BH4)4+H2→ZrB2+B2H6+6H2  (2)
The foregoing reaction equation (1) corresponds to a method in which a ZrB2 film is formed on a substrate by directly and thermally decomposing a raw material using only the thermal assist of the Si substrate heated by an appropriate means and in this case, an excellent ZrB2 film can be formed only when the substrate is heated to a high temperature on the order of not less than 550° C. On the other hand, the foregoing reaction equation (1) corresponds to a method in which hydrogen radicals are added to a raw material, a reaction of the raw material is induced by the hydrogen radical and the thermal assist of the Si substrate at a relatively low temperature (on the order of 300 to 350° C.) to thus form a ZrB2 film on the substrate. In this case, the addition of the hydrogen radical would permit the reduction of the substrate temperature or the reaction temperature required for forming a desired thin film. As an example of such a method, there has been reported one which comprises the steps of forming a ZrB2 film on a substrate, as a barrier film, at such a low temperature of about 300° C. while making use of the remote plasma CVD technique (see, for instance, J. Appl. Phys., Vol. 91, No. 6, March 2002, pp. 3904-3907 (see, for instance, p. 3904).
Incidentally, to form a thin film by repeating the formation of a mono-atomic layer by the ALD technique over desired times, it is quite desirable that the process conditions such as substrate temperature can separately and independently be set or established in the foregoing adsorption and reaction steps. However, the foregoing conventional technique never permits the separate and independent setting of such process conditions, but simply the raw and reactant gases can separately and periodically be fed to the substrate and accordingly, i.e. there is a time lag between a raw gas introduction and a reactant gas introduction, and a thin film is formed by repeatedly depositing a layer having a thickness of several atoms.
In this connection, if an ALD apparatus is so designed that it comprises a conveying chamber equipped with an evacuation means and a plurality of processing chambers are arranged around the conveying chamber so that a substrate can freely be transferred between the neighboring processing chambers by the action of the substrate-conveying means disposed within the conveying chamber, the foregoing adsorption and reaction steps may separately and independently be conducted. In this method, however, a substrate is moved between the neighboring processing chambers after once transferring the substrate to a conveying chamber. Accordingly, this suffers from such problems that it takes a long period of time for the transfer of the substrate and that this in turn makes, impossible, the reduction of the cycle time for the formation of desired thin films. Furthermore, it would be necessary for this technique to dispose a conveying chamber, and an evacuation means and a vacuum indicator for each processing chamber and this accordingly makes the structure of the apparatus complicated and considerably increases the cost required for the manufacture of the same.
In addition, the film-forming temperature is extremely high in the method for forming a ZrB2 film, as a barrier film, by directly, thermally decomposing a raw material while making use of the reaction according to the reaction equation (1) and therefore, this method would be accompanied by the foregoing drawbacks or troubles in the case of distributing wire layers of semiconductor devices in which Cu and/or Al are used as materials for the distributing wires.
Moreover, the method for forming a barrier film while making use of the reaction according to the reaction equation (2) can reduce the film-forming temperature to a level lower than that used in the reaction equation (1), but any film of, for instance, a ZrB2 film cannot be formed in fine holes having a high aspect ratio in a high coverage. In this case, the principal reaction is a gaseous phase reaction between Zr(BH4)4 and hydrogen radicals and therefore, this technique suffers from a problem in that an overhang of a ZrB2 film is formed on the upper portion of each hole or trench and in the worst case, the upper portion of each hole or trench is completely clogged.